Handle extra jars at the container implementation level so that they can be loaded in the correct classloaders

Description

Right now extra jars are added to the container's classpath used to start the container. This is not correct in some cases as it can lead to classloading issues. Each container has some specific diredctories where to put extra jars. These should be used instead.

For example, for JBoss the extra jars should be put in the server configuration dir, in the lib/ dir.